1. Field of the Invention
This invention relates to power tongs used for making up and breaking apart the threaded connections used to interconnect sections and lengths of drill pipes, casings and tubular elements of the sort employed in drilling and completing oil and gas wells.
2. Brief Description of the Prior Art
Many types of power tongs have heretofore been constructed and marketed, each having as its purpose, the engagement of drill pipes used in drilling oil and gas wells in order to permit a section of the drill pipe to be threaded up tightly into an aligned, serially connected section by means of a threaded joint. One more recent type of power tong construction which has been utilized, and which typifies other constructions in its general aspects, is that which is shown in Eckel U.S. Pat. No. 4,084,453. The Eckel power tong, as well as others now marketed, includes a frame which carries a pipe gripping and rotating mechanism. The frame and the pipe gripping mechanism include aligned throats which permit the tong to be centered around a pipe section. After such centering is accomplished by passage of the pipe section through the aligned throat sections, a partial ring carried on the power tong housing is rotated with respect to the housing in either a clockwise or a counterclockwise direction by a power unit also carried on the housing. After the ring has rotated for a certain distance, cam surfaces carried on the ring actuate link members which are carried on a die carrier also rotatably mounted on the power tong housing for rotation relative to the ring. Further and continued rotation of the ring causes the dies carried by the die carrier to engage the pipe section. After this, further movement of the ring on the housing also causes rotation of the die carrier, and the pipe section thus engaged is rotated to make up or break apart a threaded joint of pipe.
In power tongs of the type described, it has been customary to use circumferentially spaced roller bearings for the purpose of rotatably supporting and guiding during rotational movement, the power driven ring which is rotatably supported on the power tong housing. Roller bearings are also employed for supporting the die carrier for rotation relative to both the housing and the power driven ring.
The arrangement of the roller bearings described within the power tong construction is such that the roller bearings are individually and disproportionately impacted with variously differing forces as a pipe joint passes through the mouth or opening into the power tong and slams against the ring and die carrier. The forces imposed on these rollers may also be unequal during rotation of the pipe section so that one roller is loaded more heavily than the other, and thus fails at an earlier time or has a reduced or shortened service life as compared to other rollers in the set. Moreover, the rollers, in being spaced apart, do not afford continuous and firm support to the rotating mechanical elements within the power tong, and the individual rollers are susceptible to impaction by grit, grease and contact with other deleterious surfaces so that they become jammed and undergo failure due to inability to rotate during use of the tong, thus burning out individual bearings and causing the need to provide maintenance of the power tong after a relatively short time in service.
The spaced roller bearings also, in being intermittently traversed and covered by moving parts of the tong, enable a hazardous condition to exist in which the fingers of operating personnel may be caught and crushed or severely injured.